arXiv subjects

Konstantin Glukhov

Publications and source records attributed to Konstantin Glukhov.

3 recordsLinked to original sources

arXiv2023

Ordering/displacive ferrielectricity in 2D CuInP$_2$S$_6$

Using DFT-based molecular dynamics simulation of Cu$^+$ cations flipping and In$^{3+}$ cations displacive dynamics, we clarify the dipole ordering of CuInP$_2$S$_6$ ferrielectrics through the second order Jahn-Teller effect which determines the double-well potential for copper cations as well as three-well potential for indium cations inside the structural layers. The temperature dependence of the spatial distribution of Cu$^+$ and In$^{3+}$ cations is also described within the quantum anharmonic oscillators model. In$^{3+}$ cations play a decisive role in the character of the polar ordering: at ambient or for positive pressures, the first order transition occurs; with the rise of negative compression, the ferrielectric transition evolves to the second order. The peculiarities of spontaneous polarization switching are related to the contributions of copper and indium cationic sublattices.

cond-mat.mtrl-sci↗

arXiv2014

Exact ground state for the four-electron problem in a 2D finite honeycomb lattice

Working in a subspace with dimensionality much smaller than the dimension of the full Hilbert space, we deduce exact 4-particle ground states in 2D samples containing hexagonal repeat units and described by Hubbard type of models. The procedure identifies first a small subspace ${\cal{S}}$ in which the ground state $|Ψ_g\rangle$ is placed, than deduces $|Ψ_g\rangle$ by exact diagonalization in ${\cal{S}}$. The small subspace is obtained by the repeated application of the Hamiltonian $\hat H$ on a carefully chosen starting wave vector describing the most interacting particle configuration, and the wave vectors resulting from the application of $\hat H$, till the obtained system of equations closes in itself. The procedure which can be applied in principle at fixed but arbitrary system size and number of particles, is interesting by its own since provides exact information for the numerical approximation techniques which use a similar strategy, but apply non-complete basis for ${\cal{S}}$. The diagonalization inside ${\cal{S}}$ provides an incomplete image about the low lying part of the excitation spectrum, but provides the exact $|Ψ_g\rangle$. Once the exact ground state is obtained, its properties can be easily analyzed. The $|Ψ_g\rangle$ is found always as a singlet state whose energy, interestingly, saturates in the $U \to \infty$ limit. The unapproximated results show that the emergence probabilities of different particle configurations in the ground state present "Zittern" (trembling) characteristics which are absent in 2D square Hubbard systems. Consequently, the manifestation of the local Coulomb repulsion in 2D square and honeycomb types of systems presents differences, which can be a real source in the differences in the many-body behavior.

cond-mat.str-el↗

arXiv2012

Electronic Structure and Phase Transition in Ferroelectic $\rm \mathbf{Sn_2P_2S_6}$ Crystal

For $\rm Sn_2P_2S_6$ ferroelectrics by first-principles calculations an analysis of the $\rm P_2S_6$ cluster electronic structure and their comparison with crystal valence band in paraelectric and ferroelectric phases has been done and the origin of ferroelectricity has been outlined. It was established that the spontaneous polarization follows from the stereochemical activity of the electron lone pair of tin cations that is determined by hybridization with $\rm P_2S_6$ molecular orbitals. Increase of the chemical bonds covalence and their rearrangement are related to the valence band changes at transition from paraelectric phase to ferroelectric one.

cond-mat.mtrl-sci↗